This invention relates to a rotary die cutting system which is fed by web stock and more particularly to a system for reducing the scrap material produced by rotary die cutters between successive blanks treated or cut from the web.
In conventional rotary die cutter systems, wherein the web stock is fed by powered pull rolls operating in synchronism with the die and anvil cylinders, the web is fed intermittently to maintain approximately the same accumulated loop of web material.
One of the problems with this conventional technique is that after the trailing edge of the die, which includes a cut-off knife, has cut off the portion of the web which passed between the die and the anvil cylinders, momentum tends to feed the cut edge of the web forward so that there will be a substantial area of the web lying beyond the point at which the leading end of the die will again strike the web. All of the material in advance of the line where the die will make contact during the next cycle will therefore be scrap.
Accordingly, there has been a need for a mechanism which, when combined with a rotary die cutter, reduces the amount of web material that lies beyond the point where the leading edge of the die, upon rotation of the die roll strikes the web, and thereby reduces the amount of scrap web material produced. That need was initially filled by the invention of our above application, which provides for retracting the severed leading end of the web from a position beyond the nip of the rotary die cutter to a position in such relation to the nip that the leading end of the web will lie just beyond the point at which the web will be engaged by the leading edge of the die on the next cutting cycle.
Specifically, the invention of that application provides a device which includes a floating part mounted to lie on the web so that when the web is pulled forward by the pressure between the die cylinder and the anvil cylinder blanket during a die cutting cycle, the web will be sufficiently tensioned to assure an essentially horizontal position with the floating part lying on top of it. As soon as the severing cut across the web is made upon completion of the particular die cycle, gravity will cause this floating part to return to a position below the line of feed of the web, thereby retracting the severed new leading end of the web by a predetermined amount.
This retraction preferably is such that the new leading end of the web will lie just beyond, in the direction of web feed, the line at which the web will be engaged by the leading edge of the die during the next cycle. Upon engagement of the web by the die at the start of the next cutting cycle, the web loop will then again be pulled straight, which will return the floating part to its raised position during the next die cutting cycle.
In the practice of that invention, therefore, it has been found possible to reduce the amount of scrap material very substantially as compared with prior practice, but as a general rule, not to eliminate all waste. Also, while the apparatus of that invention is most successful in operation with relatively flexible web materials, it tends to be less effective in conjunction with relatively stiff web materials unless it is relatively heavily weighted.